The goal for this part of the program is the elucidation of the processes that underlie synaptic transmission in the peripheral auditory system. Our specific objective for the next grant period is to pharmacologically characterize the neurotransmitter receptors that mediate the effects of olivocochlear (OC) efferent fibers in the mammalian cochlea. While it is clear that most of the known efferent effects are mediated by acetylcholine, we know little about the receptor mediating the effects of that neurotransmitter. For instance, it cannot be said with any certainty whether the receptors are nicotinic or muscarinic. Our primary focus will be to use selective cholinergic antagonists to identify the receptor subtype(s) involved and to use this information to pharmacologically separate olivocochlear actions into distinct subcomponents. Identifying this receptor type will allow specific pharmacological antagonists to be used for the investigation and manipulation of inner ear function, will allow a better understanding of the cellular mechanism of efferent fiber action, and will lead to a better appreciation of the characteristics of efferent control over cochlear output. This information could suggest approaches to alleviating or preventing some conditions that lead to symptoms such as tinnitus and hearing loss. There may be sensorineural hearing disorders that are "transmitter-related" wherein abnormal receptor function produces inappropriate sensorineural responses.